In previous work, we compared the expression profiles of metaphase II oocytes collected from 5- to 6-week-old mice with those collected from 42- to 45-week-old mice. Among approximately 11,000 genes whose transcripts were detected in oocytes, about 5% (530) showed statistically significant expression changes, excluding a global decline in transcript abundance. Consistent with the generally accepted view of aging, the differentially expressed genes included many involved in mitochondrial function and oxidative stress. However, the expression of other genes involved in chromatin structure, DNA methylation, genome stability and RNA helicases was also altered, suggesting the existence of additional mechanisms for aging.[unreadable] [unreadable] During the last year, we examined global changes in gene expression patterns by DNA microarrays in ovaries and testes of C57BL/6 mice at 1, 6, 16, and 24 months of age. In addition, we compared a group of mice on ad libitum (AL) feeding with a group on lifespan-extending 40% calorie restriction (CR). We found that gene expression changes occurred in aging gonads, but were generally different from those in somatic organs during aging. The bulk of the changes in gonads were mostly related to gonad-specific functions. Ovaries showed extensive gene expression changes with age, especially in the period when ovulation ceases (from 6 to 16 months), whereas testes showed only limited age-related changes. The same trend was seen for the effects of CR: CR-mediated reversal of age-associated gene expression changes, reported previously in somatic organs, was limited to a small number of genes in gonads. Instead, in both ovary and testis, CR caused small and mostly gonad-specific effects: suppression of ovulation in ovary and activation of testis-specific genes in testis. Overall, the results are consistent with unique modes of aging and its modification by CR in testis and ovary.